1. Field of the Invention
The present invention relates to a vibration generator for use in a portable terminal or the like. More specifically, the present invention pertains to a vibration generator in which a vibrating body reciprocatingly vibrated by magnetic fields is supported by a leaf spring.
2. Description of the Related Art
A portable terminal such as a cellular phone or the like includes a vibration generator capable of notifying a user of arrival of an incoming call. Different types of vibration generators have heretofore been developed.
Japanese Patent Application Publication No. 2002-263557 (JP2002-263557A) discloses a vibration generator which includes a weight attached to an output shaft of a motor in an off-centered state. The vibration generator generates vibration as the motor makes rotation.
Japanese Patent Application Publication No. 2002-200460 (JP2002-200460A) discloses a technology on a vibration actuator. The vibration actuator includes a fixing portion. The vibration actuator includes a plurality of magnets and a vibrating body having a yoke for closing the magnetic fluxes generated by the magnets. The vibration actuator further includes a plurality of elastic members for movably holding the vibrating body in the fixing portion. The vibration actuator further includes a coil interlinking with the magnetic fluxes generated by the magnets. If an electric current flows through the coil, the coil generates a thrust force between the fixing portion and the vibrating body so that the vibrating body can vibrate in a specified vibration direction. In respect of the technology disclosed in JP2002-200460A, there is a demand to prevent generation of noises otherwise generated due to the severe vibration of the vibrating body. Moreover, a demand to rapidly stop the vibrating body exists in the technology disclosed in JP2002-200460A.
In order to comply with these demands, Japanese Patent Application Publication No. 2010-179295 (JP2010-179295A) discloses a technology in which vibration-proof materials made of silicon resin, urethane resin, fluorine resin, acryl, a-gel or the like are arranged at the opposite sides of a vibrating body, thereby damping the vibration of the vibrating body (see paragraph 0067 of JP2010-179295A).
In addition to the technology disclosed in JP2010-179295A, there is generally available a technology in which fluid such as grease or magnetic fluid is filled into a vibration generator. The resistance of the fluid is used to prevent undue vibration of a vibrating body or to rapidly stop the vibrating body.
In case of the technology disclosed in JP2002-263557A, it is however difficult to manufacture a motor having a stably low Q value (amplitude increasing coefficient). Accordingly, the technology disclosed in JP2002-263557A involves difficulties in improving vibration frequency characteristics and suppressing undue vibration of the vibrating body.
In case of the technology disclosed in JP2010-179295A, the vibration-proof materials are degraded over time, as a result of which the elasticity of the vibration-proof materials gets reduced. This is a cause of generating noises.
In the solution means in which the fluid such as grease or magnetic fluid is filled into the vibration generator, if the viscosity of the fluid is low, it is impossible to apply a resistance to the vibrating body. This makes it difficult to suppress undue vibration of the vibrating body. In contrast, if the viscosity of the fluid is too high, the fluid impedes the vibration of the vibrating body, consequently reducing the vibration generating characteristics of the vibration generator. In case where the fluid is used, the viscosity of the fluid varies with the change in the temperature of the vibration generator. This leads to a change in the resistance against the vibrating body. Moreover, if the fluid is used, the fluid is scattered as the vibrating body makes vibration. This poses a problem in that a Q value undergoes a change.